The present invention relates to the improvement of the rotor of the electromagnetically driven device to be supplied with a current in the stationary magnetic field so as to drive the exposure control mechanism, particularly of the rotor of the electromagnetically driven device for the shutter and/or the diaphragm by delivering a driving current to the conductor pattern coils so as to rotate the sector ring, so designed that a rotor is arranged in the gap of the magnetic field of the stator, whereby on the base plate of the sector ring, for opening and closing the shutter blades and/or the diaphragm blades conductor, pattern coils are flatly formed and the surfaces are further coated with the insulating films.
In the case of the conventional electromagnetically driven device for the shutter of the camera for opening and closing for example, the shutter blades in operative engagement of the sector ring to be rotated with the electromagnetic driving, on the upper and/or the lower surface of the sector ring formed with a thin plate consisting of insulating material, conductor pattern coils are printed, whereby the rotor is rotated in the magnetic field of the stator by delivering the driving current to the conductor pattern coils. Namely, the above-mentioned rotor is arranged in the gap of the magnetic field of the stator consisting of yokes, whereby a plural number of the magnets are arranged along the radial directions around the optical axis of the optical system around which the shutter is to be arranged. In the case of the above-mentioned construction, the power supplied to the conductor pattern coils of the rotor is proportional to the length L of the components along the above-mentioned radial directions, the magnetic flux density of the magnetic field B and the driving current I. Consequently, in order to increase the driving power, it is sufficient to increase the length L, or the current I or the magnetic field B.
However, the construction of the exposure control device for producing a large driving power in a device such as a camera whose space, weight and so on are greatly restricted, in other words, with high efficiency, is still not known.